Automatic transmissions, especially for motor vehicles, comprise, according to the state of the art, planetary gearsets which are shifted using friction or shifting elements, such as clutches and brakes, and are usually connected to a starting element subjected to a slip effect and are selectively provided with a lockup clutch, such as a hydrodynamic torque converter or a fluid clutch.
In DE 101 15 983 A1 of the applicant is described, by way of example, a multi-speed transmission comprising an input shaft, which is connected to a front-mounted gearset, an output shaft, which is connected to a rear-mounted gearset, and at least seven shifting elements whose selective shifting allows at least seven forward gears to be shifted without a range shift. The front-mounted gearset consists of one shiftable or non-shiftable planetary gearset or at least two non-shiftable mutually coupled planetary gearsets. The rear-mounted set is configured as a two-carrier, four-shaft transmission with two shiftable planetary gearset, and has four free shafts. The first of the free shafts this two-carrier, four-shaft transmission is connected to the first shifting element, the second free shaft is connected to the second and third shifting elements, the third free shaft is connected to the fourth and fifth shifting elements, and the fourth free shaft is connected to the output shaft. For a multi-speed transmission with a total of six shifting elements, it is proposed, according to the invention, to connect the third free shaft or the first free shaft of the rear-mounted gearset additionally with a sixth shifting element. For a multi-speed transmission with a total of seven shifting elements, it is proposed according to the invention to connect the third free shaft or the first free shaft of the rear-mounted set in addition to a sixth shifting element, and to connect the first free shaft in addition to a seventh shifting element.
Several other multi-speed transmissions are known, for example, from DE 101 15 995 A1 by the Applicant, in which four shiftable mutually coupled planetary gearsets and six or seven friction-locking shifting elements are provided, whose selective engagement allows a rotational speed of an input shaft to be transmitted to an output shaft of the transmission, in such a way that nine or eleven forward gears and at least one reverse gear can be provided. Two or three shifting elements are engaged in each gear according to the schematic diagram, while during a change from one gear to the respectively following higher or lower gear, only one engaged shifting element is disengaged in order to prevent range shifting and a previously not engaged shifting element is provided.
In the related unpublished patent application DE 10 2005 002 337.1 of the applicant is furthermore proposed a multi-speed transmission with an input shaft, an output shaft, four mutually coupled separate planetary gearsets and five shifting elements, in which eight forward gears can be shifted without range shifting, that is, in such a way that during a change form a forward gear into the following higher or lower forward gear, respectively only one of the previously engaged shifting elements is disengaged and only one previously disengaged gears is engaged. The multi-speed transmission has also a reverse gear. Three shifting elements are respectively engaged in all forward gears and in the reverse gear. With regard to a kinematic coupling of the four planetary gearsets among each another and to the input shaft and output shaft, it is provided that a carrier of the fourth planetary gearset and the input shaft are connected to each other and form a first shaft of the transmission, a carrier of the third planetary gearset and the output shaft are connected to each other and form a second shaft of the transmission, a sun gear of the first planetary gearset and a sun gear of the fourth planetary gearset are connected to each other and form a third shaft of the transmission, a ring gear of the planetary gearset forms a fourth shaft of the transmission, a ring gear of the second planetary gearset and a ring gear of the third planetary gearset are connected to each other and form a fifth shaft of the transmission, a carrier of the first planetary gearset and a ring gear of the third planetary gearset are connected to each other and form a sixth shaft of the transmission, a sun gear of the second planetary gearset and a ring gear of the fourth planetary gearset are connected to each other and form a seventh shaft of the transmission, and a carrier of the second planetary gearset forms an eighth shaft of the transmission. With regard to the kinematic coupling of the five shifting elements to the four planetary sets and to the input shaft and output shaft, it is provided that the first shifting element is arranged within the direction of power flow between the third shaft and a housing of the transmission, the second shifting element is arranged between the fourth shaft and the housing of the transmission, the third element is arranged between the first and fifth shaft, the fourth shifting element is arranged either between the eighth and second shaft or between the eighth and the sixth shaft, and the fifth shifting element is arranged either between the seventh and fifth shaft or between the seventh and eighth shaft or between the fifth and eighth shaft.
Automatically shiftable motor vehicle transmissions of planetary construction have already been frequently described in the state of the art and are being constantly further developed and improved. These transmissions should thus have a sufficient number of forward gears as well as a reverse gear with a transmission ratio with a high overall spread that is well suited for motor vehicles as well as very advantageous progressive ratios. These should furthermore make possible a high startup transmission ratio in the forward direction and include a direct gear as well as be suitable for use in passenger cars as well as in commercial vehicles. These transmissions should furthermore require a low construction expenditure, In particular a small number of shifting elements, and prevent double shifting in sequential shifting mode, so that only one shifting element is changed during shifting into defined gear groups.
It is an object of the invention to propose a multi-speed transmission of the type mentioned above with at least eight shiftable forward gears without range shifting and at least one reverse gear, the lowest possible number of shifting elements is required when utilizing a total of four planetary gearsets. The transmission should, in addition, have a large ratio spread with comparatively harmonious gear gradation and an advantageous efficiency at least in the main travel gears at least, that is, comparatively low drag and gearing losses.